Field of the Invention
The present invention relates to a solid-state imaging device and an imaging system.
Description of the Related Art
In recent years, an imaging system such as a digital video camera and a digital camera becomes widespread commonly, which uses a CMOS image sensor therein that is suitable for low power consumption and high-speed readout. In the CMOS image sensor, a sequentially reading out operation (rolling shutter operation) is basic which sequentially reads out pixels in every one row or in every block of several rows, but a CMOS image sensor having a function of a whole-pixel simultaneous electronic shutter is also proposed (refer to International Publication No. WO 11/043432)). Here, the whole-pixel simultaneous electronic shutter is a mechanism of simultaneously controlling the start and end of exposure with light in all of the pixels.
When the area of a charge holding portion is widened or the impurity concentration of the charge holding portion is increased so as to ensure a sufficient amount of saturation electric charges, in the CMOS image sensor, there has been the case where a dark current noise increases which is generated in the charge holding portion and an image quality lowers. In particular, when the whole-pixel simultaneous electronic shutter operates, time periods during which the charge holding portions of the pixels hold signal charges result in being different from each other. Because of this, when the dark current noise is large which is generated in the charge holding portion, the amount of the noise results in being different depending on the positions in the image, and there has been a possibility that a remarkable noise such as shading occurs. In addition, even in the case where the whole-pixel simultaneous electronic shutter is not operated, it is desired that the dark current noise is reduced which is generated in the charge holding portion.